A spokesperson for the US Department of Homeland Security (DHS) described the incident an "apparent act of terrorism".

"We have recently seen attacks like this one throughout the world. DHS and its law enforcement partners remain vigilant and committed to safeguarding the American people," the spokesperson said in a statement.

US President Donald Trump was briefed about the incident, Sarah Huckabee Sanders, White House press secretary, said in a statement.

"Our thoughts and prayers are with all those affected," she added.

Even though police said the investigation was still pending and there was no claim of responsibility, Trump later tweeted that the US "must not allow ISIS to return, or enter, our country after defeating them in the Middle East and elsewhere", referring to the Islamic State of Iraq and the Levant armed group, also known as ISIL.